The manufacture of microelectronics has become a major worldwide industry. A typical process in manufacturing a microelectronic component includes securing a semiconductor chip or die on a circuit board/interconnect substrate. Small wires, welded into place using an automated welding process known as wire bonding, connect the electronic circuitry on the chip to circuitry on the circuit board/interconnect substrate. Such a process permits complex circuits to be made in a more standard durable package.
One issue that is of particular concern to the microelectronics industry is reverse engineering. Using readily available equipment, it is possible to analyze in detail the layout of a chip's circuitry and then copy the design for use in a competing product. Because reverse engineering a chip is significantly less expensive and may require less technology than designing a competing chip from scratch, the incentive to reverse-engineer a semiconductor chip is very great.
Various methods of defeating reverse engineering have been proposed. One such method is to cover a chip with an impermeable coating, such as a thermal spray, and then cure the coating using a predetermined cure schedule. The coating prevents analysis of the circuitry on the chip and cannot be removed without completely destroying the circuitry. One challenge of using impermeable coatings is that the ideal materials for such a coating behave quite differently from the silicon-based chip. Of particular concern is the difference in the coefficient of thermal expansion coupled with the high elastic modulus of each of the many materials involved. If the difference between the materials' coefficients of thermal expansion is too great in relationship to the modulus of the materials, a stress state of the material system develops that may be higher than what the strength of the circuitry can handle, therefore the circuitry becomes damaged. A chip exposed to this stress state in the application stage, in the curing stage, or in the field life may be adversely affected with respect to performance and may encounter unacceptable failure rates of the microelectronic chip or module.
Another issue, unrelated to reverse-engineering concerns, is that the top layer of microelectronic circuit lines on the chip is not designed to be resistant to aggressive scratching, impact, or temperature change. Even incidental contact with the chip may cause a failure of part of the circuitry in the chip.
Thus, it is desirable to protect a semiconductor chip from damage and protect the integrity of a semiconductor chip or module while preventing the chip or module from being reverse-engineered.